DE1646794A1 - Process for the production of high-strength carbon threads - Google Patents

Description

Patent attorneys.

Dipl.-Ing.R.Beetzu. ₂₉ ^ .- - '- November 16, 1966

Dipl.-Ing. Lamprecht jx / 2366/06 "

T646794

National Research Development Corporation, London, S, W.l (Great Britain)

Process for the production of high-strength carbon thread

The invention relates to a method of manufacture ™ high-strength carbon fibers or threads by coking fibers or threads of an organic polymer.

A process for the production of carbon threads starting from fibers or threads of an organic polymer by coking has already been described in an earlier patent application N 26 625 VIb / 80b dated 23-, 1965 by the applicant.

In general, such procedures in order thereon were od enfewickeltj carbon fibers, it yarns produce, like the so well liohe a tensile strength (ultimate tensile strength) than

ί ■■ '■ "-'" ■ '.- / ν

also have a high value of the Young's modulus (E).

So FOr some applications would be desirable, however, carbon fibers or threads which exhibit both high tensile strength and high Zugspannungscharakteristiken, ie carbon fibers or filaments that have some ability to stretch tind but a useful tensile strength maintain aeden carbon, which be able to stretch noticeably before breaking *

109838/0241

BADORfGlNAL

In processes that lead to solid carbon threads, it is possible to increase the Young's modulus at different tensile stress values, with a corresponding reduction in the breaking strain. If, however, the threads or fibers are subjected to continued or further treatment up to very high tensile strength values, it is possible to reach a point at which the elongation assumes a maximum value; up to this point the tensile strength increases more or faster than the Young's modulus, while beyond this point the Young's modulus increases more or more rapidly than the tensile strength, which can in fact decrease. that one continues the production of carbon fibers or filaments by converting polymer fibers or filaments and ends or terminates in the vicinity of such a maximum value of the elongation at break, whereby high fourths both ß $ j? Elongation at break (ultimate tensile strain) as well as tensile strength (ultimate tensile stress) can be achieved. ■. , _;

A further post-treatment or the carbon filament at a temperature above coking temperature in an inert atmosphere, such as in argon, increase the Young's modulus and the tensile strength steadily more quickly and can rise high up to a point, beyond which the tensile strength increases less rapidly ■ , may decrease as the Young's modulus or in fact; to ^_this: Point, the elongation at break has a maximum value. ^r Such Naefrbe- 'action to the vicinity of this point, therefore, * is a further feature of the invention. .

109836/024 1

-y-

That in the already mentioned old application N 26 625 VIb / 80b The process described by the applicant for the production of high-strength carbon fibers or threads consists in a combined application of heat and tension during the transformation of Fibers or threads made of organic polymers, such as polyacrylonitrile, to carbon fibers or threads. This transformation includes that Heating the polymer fibers or filaments to a coking temperature in a non-oxidizing atmosphere, such as in hydrogen, and, if necessary, a preceding oxidation treatment at a relatively low temperature, such as, for example, heating in air or preferably in an oxygen-rich atmosphere. This pretreatment, if used, should last as long take time that a complete penetration of the individual threads or fibers is ensured by the oxygen, so that no soft core remains, which is disadvantageous for the behavior of the carbon fibers or threads obtained at the end of the process •were. The interaction of heat and tension can occur during the high temperature coking or during the pretreatment, if such takes place, or is provided during both will.

In a special way of carrying out the process for the production of carbon fibers or threads described in the patent application mentioned, polyacx'ylnitrllfibers held under tension are first heated in an oxidizing atmosphere to 200 to 250 ⁰ G for a time that

109836/0244

BATH

sufficient to allow substantially complete permeation of oxygen through the individual fibers or filaments and the fibers thus formed to a coking temperature of at least 1000 ⁰ G are heated under non-oxidizing conditions below.

The applied tensile stress is such that longitudinal shrinkage, those normally during this previous low temperature oxidation process would take place, are at least reduced or no longer occur, or in such a way that that an elongation of the fibers is effected. The previous one Low temperature oxidation treatment. can by heating the _ Threads or fibers are made in an oxygen-rich atmosphere be or in commercially pure oxygen, the Fibers or threads from each other at such a distance that a free passage of oxygen between them is possible ο

According to this process, high-strength carbon fibers or threads are achieved and there is also a further aftertreatment of the carbon fibers or threads in an inert Atmosphere, for example at 2500 C in argon, by which the Young's modulus without increasing the tensile strength is increased. ' -

In a particular method according to the present invention for making carbon fibers or filaments

109836/0241 BADORK ₃₁ NAL

maximum strength and. maximum elongation at break exists Post-treatment in heating the high-strength carbon fibers or threads in an inert atmosphere, such as argon, for at least one hour at temperatures between 1300 and 180.0 ° 0.

"Before the conversion process described above, you can the fibers or threads are stretched or stretched, namely stronger than in the manufacture of polyacrylonitrile fibers for Commonly used for textile purposes. . V. ■

In an example of the inventive method were polyacrylonitrile fibers or filaments of 20 λχ diameter in air for 44 hours at 220 ⁰ C is heated and held under tension. The fibers or threads were then coked by heating to a temperature of 1000 C in a hydrogen atmosphere. The resulting fibers or filaments were then subjected to a heat treatment as shown in the following table, and the results summarized below were obtained.

3838/0 241

BATH ORIGINAL

ι arm hand
at T ⁰ C lung tensile strenght
(TS)
ρ
kg / cm 100O ⁰ C l4.8xl0 ³ 1500 ° C 22.5XlO ³ 2000 ° C 19, OxIO ³ 2500 ° C
2800 ° C ■ 5
17.93x10
17.86xlO ³

Young fiber

kg / cm

1.65xlO ⁶ 2.46x1O ⁶

Elongation at break ^

TS E _v mod)

3, B7xlO ^C 4.22x10 ^

o.9i 0.59 0.46 0.42

In another example, carbon fibers or filaments having an average diameter of from 12 7yu / U - PoIyacrylnitril or threads made, by five hours long heating in air at 220 ⁰ C, vmrde v / obei shrinkage thereby preventing the threads were wound onto a bobbin or a shaped body, for example. The "oxidized" threads were then coked up to 1000 ° C and subjected to a heat treatment, the data of which can be found in the table below:

poor hand!
at T ° C Lung tensile strength
(TS)
kg / cm Young
Module (ξ)
parallel
fiber
ρ
kg / cm TS / E (rnod) 1000 ° C
1200 ° C l8,3xio ³
l6,7xio ³ 1.85x10 °
2, ΐβχ10 ° 0.99
0.77 1300 ⁰ C 20.6-10 ³ 2.21x10 ° - - 0.93 14OO ° C 28.8-10 ³ D. 1.24 1500 ⁰ C '3ΐ, 2χΐθ ³ 6th
2.37x10 1.32 1600 ° C . 32.7χΐθ ³ r- 6 1.28 1700 ⁰ C 20.6XlO ³
109836/0241 2, υ7χ10 ^ϋ 0.99
BATH ORIGINAL

From the table above it follows that both the tensile strength as well as the elongation at break within the temperature range from I5OO to I800 C for maximum heat treatment Achieve values. ■

According to the invention, so carbon fibers or threads with the desired properties of high tensile strength and at the same time high elongation at break can be produced.

109836/024

Claims (1)

Claims 1. Process for the production of carbon fibers or filaments high strength through conversion of fibers or threads of an organic polymer through coking in the course of a heat treatment * thereby marked, that the treatment after the actual coking up to the highest possible fourth of the tensile strength continues, but breaks off when a maximum value of the elongation at break is reached .: or the thread obtained after coking a corresponding one subject to limited follow-up treatment. 2. The method according to claim I, characterized by an aftertreatment the carbon fibers or threads by heating in an inert atmosphere above the coking temperature to increase the tensile strength and Young's modulus, the Temperature is limited to a value at which one is close reaches a maximum value for the elongation at break. ^. Process according to claim 1, characterized in that one the fibers or threads of the polymer, in particular of polyacrylonitrile, in a first stage in an oxidizing atmosphere a temperature below the coking temperature to complete Penetration of the fibers or threads is heated by oxygen, then coked in a second stage at a coking temperature in a non-oxidizing atmosphere, the Fibers or threads at least during one of these stages of the 109836/0241 BATH ORIGINAL copy combined exposure to heat and tension that is at least sufficient! the normal shrinkage of the fibers and that the carbon fibers or filaments can then be increased to an even higher level in an inert atmosphere Temperature heats up to increase the tensile strength and the Young's modulus, with the reached end temperature just below the one at which the Young's modulus begins to increase more rapidly than the · tensile strength .. · -. 4. The method according to claim J,. Characterized in that the Final temperature in an inert atmosphere in the range of 1200 up to 1700 C. 109836/0241 BATH ORIGINAL